tough question

Two disks are spinning freely about axes that run through their respective centres (see figure below). The larger disk

(R1 = 1.42 m)

has a moment of inertia of 1180 kg · m2 and an angular speed of 4.0 rad/s. The smaller disk

(R2 = 0.60 m)

has a moment of inertia of 906 kg · m2 and an angular speed of 8.0 rad/s. The smaller disk is rotating in a direction that is opposite to the larger disk. The edges of the two disks are brought into contact with each other while keeping their axes parallel. They initially slip against each other until the friction between the two disks eventually stops the slipping. How much energy is lost to friction? (Assume that the disks continue to spin after the disks stop slipping.)

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Apply to eng grad school, will bad Phys lab grade affect this?

I am currently a senior at a no name liberal arts college studying math and physics. I am unsure about want I want to do in the future, but I am considering engineering for graduate school in the far future. Field yet to be determined.



Last year I took an advance physics lab course and absolutely bombed the class because I bit off more than I could chew in terms of all the classes I was taking. I ended up with a C for a final grade :(*



I don't really want to take the class again because I really didn't like it. Next semester is the last chance I have to retake it in hopes of getting a better grade. My question is, is it worth retaking? Will engineering graduate schools really care that *I bombed one class if I did well in all my other classes? Will I still have a good shot at getting into the top 75 engineering grad programs with this one C? I'd prefer not to take the class again, especially final semester of senior year, because it's a lot of work.*



Just to give you some background, I've gotten A's and A-'s in all of my other physics classes. Similar with math (except 1B and 1 B-). My GPA is 3.72.

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Work Energy- Tension

1. The problem statement, all variables and given/known data

A 1.3kg stone is whirled in a vertical circle at the end of a 0.83m long string. The tension in the string at the top of the circle is 6.4N. What is the tension in the string when the stone is at the bottom of the circle?



2. Relevant equations

F_c= ma_c

W=|F||Δd|cosθ



W_ALL= E₂- E₁



E= 1/2 mv²- mgh



3. The attempt at a solution

I think I'd have to find the speed of the stone at the bottom of the circle first but I'm not sure how to start it.

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Does there exist a transformation between a loop and a close loop ?

Dear All:

For a loop structure(say a very long atomic chain) and a closed loop structure( connect the head and tail of this atomic chain). Does there exists a transformation between these two structures?

For example if we want to study the vibration mode of these two cases. If we already know all the modes of one case then are we able simultaneously know the information of the other without any further calculation?



Best Yen

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Want to go to eng grad school, will a bad lab grade affect this?

I am currently a senior at a no name liberal arts college studying math and physics. I am unsure about want I want to do in the future, but I am considering engineering for graduate school in the far future. Field yet to be determined.



Last year I took an advance physics lab course and absolutely bombed the class because I bit off more than I could chew in terms of all the classes I was taking. I ended up with a C for a final grade :(*



I don't really want to take the class again because I really didn't like it. Next semester is the last chance I have to retake it in hopes of getting a better grade. My question is, is it worth retaking? Will engineering graduate schools really care that *I bombed one class if I did well in all my other classes? Will I still have a good shot at getting into the top 75 engineering grad programs with this one C?*I'd prefer not to take the class again, especially final semester of senior year, because it's a lot of work.*



Just to give you some background, I've gotten A's and A-'s in all of my other physics classes. Similar with math (except 1B and 1 B-). My GPA is 3.72.

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Higher social class predicts increased unethical behavior

Quote:

Seven studies using experimental and naturalistic methods reveal that upper-class individuals behave more unethically than lower-class individuals. In studies 1 and 2, upper-class individuals were more likely to break the law while driving, relative to lower-class individuals. In follow-up laboratory studies, upper-class individuals were more likely to exhibit unethical decision-making tendencies (study 3), take valued goods from others (study 4), lie in a negotiation (study 5), cheat to increase their chances of winning a prize (study 6), and endorse unethical behavior at work (study 7) than were lower-class individuals. Mediator and moderator data demonstrated that upper-class individuals’ unethical tendencies are accounted for, in part, by their more favorable attitudes toward greed.

http://www.pnas.org/content/early/20...73109.full.pdf

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When can the solution to the Schrodinger equation be discontinuous?

If I have a solution to the time-dependent Schrodinger equation



[tex]

i \frac{\partial \psi(x,t)}{\partial t} = \left( -\frac 12 \Delta_x + V(x) \right) \psi(x,t)

[/tex]



and the potential is infinitely differentiable with compact support, then I know that [itex]\psi[/itex] has a continuous first derivative, right? In fact, doesn't the SECOND spatial derivative have to exist for this function, so that the first derivative also needs to be DIFFERENTIABLE? Or am I missing something?

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Force Body Diagram

Hello,



I have been assigned a project to find a device to improve on, and one of the tasks is to create a force body diagram. I have a little bit of confusion when it comes to drawing it because if I'm writing the paper on shoes, and how it improves the movement of the feet, how will the free body diagram look?



I understand that in able for your whole body to move, you have to consider the frictional force, applied force, and the normal force. Does that include the forces exerted from the ground?



Also if you were to focus the force body diagram primarily on the feet, what would the forces be applied when you are walking/running? Would the forces change depending on the structure of the shoe that is being worn? How would you get the magnitudes of the forces?



Please help!

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Real analysis

The problem statement, all variables and given/known data



Show that if ##f:\mathbb{R}\to \mathbb{R}## is a polynomial function of odd degree, then ##f(\mathbb{R}) = \mathbb{R}##.



The attempt at a solution



How can I rigorously prove this? What is the most direct and concise way to prove this?



What I have is the following:



Any polynomial in ##x_1, x_2, \ ... \ ,x_n## with coefficients in ##\mathbb{R}## is continuous. Since ##\mathbb{R}## is connected, ##f(\mathbb{R})## is connected, thus we can apply the intermediate value theorem. Now any polynomial of odd degree has at least one real root thus there exists ##p,q\in \mathbb{R}##, ##p<q## such that ##f(p)<0## and ##f(q)>0##. Thus we can then choose ##p\in \mathbb{R}## such that ##f(p)\ge 0##, ##f(p) \le 0## and obtain any ##f(\mathbb{R})\in \mathbb{R}##. Therefore, ##f(\mathbb{R})\in \mathbb{R}.##

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Vapor composition from bubble-point temp.

Suppose you have a mixture of 30 mol% pentane and 70 mol% hexane at 1 atm and 60^oC.



If the T_bubble-point = 55.1^oC, calculate the composition of vapor of the first bubble as the mixture is heated.



I found p^*_pentane = 1392.95 and p^*_hexane = 484.96 using Antoine's equation with T = 55.1.



Now I suppose I must use Raoult's law as:



y_aP = x_ap^*_a(@55.1^oC)



Using this I get x_pentane = (0.7*760)/1392.96 = 0.382



However, the answer sheet says x_pentane = 0.55.



Can anyone figure where I'm mistaken?

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Kirchoffs Laws

1. The problem statement, all variables and given/known data



I need to find all the values essentially across the entire circuit



2. Relevant equations



Kirchoffs First and Second Law



3. The attempt at a solution



Attempted to find currents and resistance multiple time; didn't know how to work with the two power sources or the capacitor



An explanation of the assignment can be found here, along with a diagram of the circuit

Attached Images

vjae.png (20.5 KB)

Attached Files

KirchoffsLaws.pdf (145.3 KB)

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Why Do DC Brushless Motors Need Hall/EMF Sensors?

I understand the basic gist of the whole DC brushless motor, but I don't understand why there needs to be a sensor. Why can't the controller just alternate between phases at a constant rate? What I mean is that if there are a fixed number of ways the coils can be charged, why not just alternate between them and keep going? I hope my question makes sense.

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Mechanical Energy- Orbit

1. The problem statement, all variables and given/known data

What is the total mechanical energy of a 380kg satellite in a circular orbit 3.0 Earth radii above the surface?





2. Relevant equations

W= E₂- E₁



E= 1/2 mv²- [itex]\frac{GmM}{r}[/itex]





3. The attempt at a solution



I'm not sure if the equations above are suitable to solve this or I just don't understand how to start the question.

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Simple question about fourier series

Hello,

Find the Fourier serie of f(x)=|sin(x)| on the interval (-1,1)



I'm just a little confused, does that mean that I have to integrate from -1 to 1 to find the coefficients ? Because the formula of the coefficients is in terms of the period T, for this function the period is pi. Or do I have to consider it only in -1,1 and take the period T=2 ?



Thanks

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Solve the log equation...

1. The problem statement, all variables and given/known data

Solve the logarithmic equation for x:

Log₂ (x^2 - x - 2) = 2



2. Relevant equations







3. The attempt at a solution



I'm just totally lost on how to even start...

1. The problem statement, all variables and given/known data







2. Relevant equations







3. The attempt at a solution

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Finding work to do research on

As an undergraduate, how does one generally go about searching for summer research positions? I am interested in applying to a much wider range than the programs my school offers, so does anyone know how or where I might perform a search for opportunities to do research?



Thanks!



BiP

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